Modelling the spectral selective solar absorption properties of graphite–silica composite/aluminium structures

• Modelling of optical properties of graphite–silica composites using Bruggeman theory
• Performance contour plots of graphite–silica composite/aluminium solar absorbers
• Procedure for designing anti-reflection coating is presented.

Calculation of the index of refraction of graphite–silica composites has been performed using Bruggeman's theory for randomly oriented nano-graphite grains in silica. Subsequently the normal incidence reflectance from graphite–silica composite/aluminium and anti-reflection coating/graphite–silica composite/aluminium structures was performed using the transfer matrix formalism. The solar performance (absorptance, emittance, and efficiency) of the graphite–silica composite/aluminium structures is calculated with respect to composition and thickness of the graphite composite layer (and presented in the form of contour plots) and is compared with experimental data. We show that the combined contour plots are consistent with experimental data only within a small range of volume fraction and thickness of the composite layer. Further, we present analytic relations for the near optimal index of refraction and thickness of the anti-reflection coating for the graphite–silica composite/aluminium structure.